It basically gives a unique ID number to each copy of an active object of the same type. So spreading the value 1 in alterable value A in the active object "Runner" would uniquely identify each instance of "Runner" with the values 1 to the number of total Runner objects. The object with value 1 would be the first created instance (first one you placed in the level editor, or first created by a create action if none are in the level editor) and the instance with the highest value would be the last created instance.

In this game, qrleon uses the spread value function to give each runner a different horizontal speed (Always: x("Runner") = x("Runner") + Alterable Value A("Runner")) without requiring a lot of separate active object types or code.

It's also occasionally useful to positively identify specific instances by an ID number (using the alterable value A of Runer == XX condition).

Spreading a number over an alterable value of an active object assigns a different value to each instance of that object. (0,1,2,3,4,5, etc)

This can be used to identify individuals and allows the programmer more control over each object. That is, the programmer can create different events to effect multiple instances of an object differently based on it's unique ID variable.

alterable value A of ("Invader")= 1
("Invader") overlaps ("Bullet")
--> Destroy ("Invader")

alterable value A of ("Invader")= 2
("Invader") overlaps ("Bullet")
--> Destroy ("Bullet")

I'm not sure if that makes sense? It was kind of a horrible example, but I couldn't think of anything better on the spot. :P

//edit//

I think I must type slow or something... geez, everyone answered before me! :D

Haha all this time I've been writing "repeat # of objects times" and incrementing a counter to do that. It doesn't really save me that much time, other than moving that in to my level start event, and happening in one frame. How about those internal flags? Anybody use them much?

And in return for answering my question, I'll mention that you can set preferences for the event editor, such as shrinking the size of the event grid icons, switching to all text, or even turning off automatic event generation for the default movements (handy if you don't want to keep deleting default actions every time you want to do something custom). You can even set KnP up to load directly to making a new game.